Analytical and Probabilistic Correlations Between In-Situ Tests and Instantaneous Logging-Paper

Paper

Pdf Summary

The study evaluates whether Measurement While Drilling (MWD) data can help estimate soil strength during geotechnical investigations. Researchers analyzed approximately 100 boreholes across 30 sites in France, covering soils including clay, gravel, compact sand, chalk, and limestone. More than 90% of the boreholes used rotary drilling.<br /><br />The analysis focused on a modified Somerton Index, derived from drilling push force and penetration rate, and compared it with pressuremeter limit pressure. Because drilling readings are affected by equipment performance, sensor sensitivity, fluid temperature, tool type, and operating method, the researchers introduced a borehole-specific correction based on calibration measurements taken before and after drilling. The correction normalizes the measured index against the machine’s baseline response, reducing equipment-related bias.<br /><br />Before correction, the Somerton Index and pressuremeter results often showed similar trends but differed substantially in scale. After correction, their alignment improved, and rotary-drilled boreholes showed a strong, approximately linear relationship between the corrected index and pressuremeter limit pressure. The findings support the corrected index as a potentially useful indicator of soil resistance and a cost-efficient complement to conventional in-situ testing.<br /><br />The method is most reliable in rotary drilling. Its performance is limited in rotary-percussive drilling, where impact forces are not represented by static calibration. Results may also be less dependable in heterogeneous or very hard soils, particularly when drilling equipment lacks sufficient power. The authors emphasize that consistent drilling methods, push force, and fluid temperature are important for valid calibration. Overall, calibrated MWD data can improve subsurface characterization, but interpretation must account for geological and operational conditions.

Keywords

Measurement While Drilling

MWD data

soil strength

geotechnical investigations

Somerton Index

pressuremeter

borehole calibration

rotary drilling

drilling correction

subsurface characterization